1. Field of the Invention
The present invention relates to lines for the transmission of electrical energy and signals, and more particularly to selective absorption conductors of the kind which selectively provide an impedance and an absorption determined within a chosen range of high frequencies. The present invention further relates to transmission cables, with several conductors, devices to transmit a certain range of frequencies, such as cables designated to attenuate certain frequencies, specially so called low pass lines, and certain types of filters.
2. Description of the Prior Art
Low pass cables have been described in both the trade literature and in various patents, including my own. Generally, their purpose is to conduct without attenuation lower frequencies such as 60 Hz line voltages, from an outlet source to a receiving appliance. However, the presence of RFI or other high frequency noise signals on such cables is to be prevented, because of compatability problems between a noise source and a noise succeptable receiver. Common examples of compatability problems are the disruptive effect that the turning on of household appliances such as an electric razor may have on a television, or a welding robot on microprocessor controls for operating the robot, and so forth.
In order to promote compatability between noise sources and succeptable receivers, lumped component filters are often used.
On the other hand, selective absorbent conductors and lines employing a distributed filtering effect are known, and described in my U.S. Pat. Nos. 3,191,132 and 3,309,633, in which dissipation is obtained by employing magnetic and dielectric lossy composite material as insulation. More especially, my U.S. patent application Ser. No. 855,593, now abandoned, continued as Ser. No. 202,654, filed Oct. 1, 1980, describes a more recent invention with the use of an improved lossy material of that kind. Such lossy cables, are specified, for military and space applications, by Standard MIL-C-85485 of Sept. 16, 1981.
Selective absorbent conductors and lines of another kind, are known and described in my U.S. Pat. No. 3,573,676, in which selective absorption is obtained by employing an "artificial" or "enhanced" skin effect.
Both dissipation technologies are based upon higher frequency physical effects, like magnetic losses in magnetic materials, and skin effects and do not permit reaching appreciably lower frequency (under 10 MHz or even 1 MHz, for example) range, where the mentioned physical phenomena cannot be used (magnetic absorption) or are difficult to implement for practical structures (artificial skin effect).
Thus, the cables noted above do show sufficient absorption in the higher frequency ranges, such as above 30 Mhz where the effects of magnetic absorption exist. This is related to the magnetic loss angle, or .mu.", the reactive part of magnetic permeability. However, there is a present need for a cable or transmission line exhibiting increased attenuation at lower range R.F. frequencies, that is in the 10 Mhz, or even 1 Mhz, range, which cannot be achieved by means of above mentioned effects.